1. Field of the Invention
This invention relates generally to branch pipe lining techniques, and more particularly, to a pipe lining method which is implemented using a main pipe liner bag.
2. Description of the Related Art
When an underground pipe, such as pipelines and passageways, becomes defective or too old to perform properly, the pipe is repaired and rehabilitated without digging the earth to expose the pipe and disassembling the sections of the pipe. This non-digging method of repairing an underground pipe has been known and practiced commonly in the field of civil engineering. The pipe lining method utilizes a tubular pipe liner bag made of a resin-absorbent material impregnated with a hardenable resin, and having the outer surface covered with a highly air-tight plastic film. The tubular pipe liner bag is inserted into a pipe to be repaired by means of a pressurized fluid such that the pipe liner bag is turned inside out as it proceeds deeper in the pipe. Hereinafter, this manner of insertion shall be called "everting." When the entire length of the tubular liner bag is everted (i.e., turned inside out) into the pipe, the everted tubular liner is pressed against the inner wall of the pipe by a pressurized fluid, and the tubular flexible liner is hardened as the hardenable resin impregnated in the liner is heated, which is effected by heating the fluid filling the tubular liner bag. It is thus possible to line the inner wall of the defective or old pipe with a rigid liner without digging the ground and disassembling the pipe sections.
The foregoing pipe lining method can be similarly applied to the lining of a main pipe of sewerage pipes or the like and a branch pipe branched off the main pipe.
When a main pipe is lined using a main pipe liner bag by the pipe lining method as mentioned above, an opening of a branch pipe toward the main pipe (branch pipe opening) is covered with the main pipe liner bag, so that a portion of the main pipe liner bag covering the opening must be cut away. Conventionally, this cutting operation has been performed by means of a cutting robot which is remotely controlled on the ground to drive a cutter mounted thereon.
However, the cutting operation through the remote control of the cutting robot for cutting a main pipe liner bag along an opening of a branch pipe requires much experience. It is generally difficult to precisely cut a main pipe liner bag along an opening of a branch pipe with a cutter through remote control, and therefore, an inner wall of the branch pipe, more specifically a periphery of the branch pipe opening toward the main pipe, is likely to be damaged by the cutter, and the cutter itself, as the case may be, may also be significantly broken.